Temperature measurement is required by a wide range of activities and processes, and a large variety of devices are available for measuring temperature for different applications, temperature ranges and environmental conditions. Non-invasive devices for measuring temperature of a material usually measure temperature of the material at or near a surface of the material. Generally, measuring internal temperature of a material involves accessing an internal region of the material invasively and determining a temperature for the internal region. There is an ongoing need for new and alternative methods and devices for accurately measuring temperature conveniently and accurately.
It is well known that absorption of light by water is a function of temperature and that the shape of the optical absorption spectrum of water is a function of temperature. For example, U.S. Pat. No. 6,115,673, the disclosure of which is incorporated herein by reference, discusses how peaks in the water absorption spectrum centered at 2500 nm, 1950 nm and 1450 nm affect IR spectroscopy and how the positions of the centers of the peaks and magnitudes of the peaks change with temperature. The patent notes that the temperature dependence of the absorption spectrum “greatly hinders” near IR spectroscopy.
However, whereas, it is known that the absorption spectrum of water is dependent on temperature, it appears not to be known to determine temperature of materials comprising water by measuring the absorption spectrum of the water they comprise. Since, in general an absorption spectrum of a material is dependent upon many different components of the material, it may not have appeared to be practical to use absorption measurements of a single component, such as water comprised in the material to determine the material's temperature.